The present invention generally relates to magneto-resistance effect magnetic heads. More particularly, the invention relates to a magneto-resistance effect thin films as a component of a magneto-resistance effect device.
A magneto-resistance effect magnetic .head (MR head) employed as a playback head in a hard disc drive device, will have a magneto-resistance effect device (MR device) sandwiched between a pair of magnetic shield cores, with a non-magnetic layer in-between. The magnetic shield cores will be arranged with a gap therebetween on a medium-facing surface of the MR head.
With such an MR head, excess external magnetic field is shielded by the pair of magnetic shield cores in order to cause only the target external magnetic field to enter the MR device. Information signals are reproduced by taking advantage of the change in the resistance of the MR device caused by the external magnetic field. The gaps defined by the non-magnetic layers between the MR device and magnetic shield cores are termed playback gaps.
An MR device generally is comprised of two layers of magneto-resistance effect thin films (MR thin films) laminated with an insulating layer in-between. A forward electrode and a rear electrode are connected to the medium-facing side and the opposite side of the MR device, respectively. Sense current is caused to flow through these forward and rear electrodes. The MR head, the MR device of which has two MR thin films laminated one on the other with the insulating film in-between, is effective in suppressing Barkhausen noise and external static electricity.
The principle of reproduction by the MR head is shown in FIG. 5. If a sense current is caused to flow through two MR thin layers 101 and 102 in a direction x, magnetic fields, shown by arrows Hs.sub.1 and Hs.sub.2, are generated in the MR thin films 101 and 102, respectively, and this shown in FIG. 6, so that the direction of magnetization of the MR thin films 101 and 102 as indicated such as Mo.sub.1 and Mo.sub.2, which have directions .phi..sub.1 and .phi..sub.2 corresponding to the direction x of the sense current.
If an external magnetic field shown by arrow Hex is now applied to the MR thin films 101 and 102, the directions of magnetization of the MR thin films 101 and 102 are rotated to those indicated by arrows Mo.sub.1, Mo.sub.2, respectively. The angles .THETA..sub.1 and .THETA..sub.2 included between the directions of magnetization Mo.sub.1 and Mo.sub.2 and the direction x correspond to the values of the strength of the magnetic fields applied to the MR thin films 101 and 102. The result is that the values of the electrical resistance of the MR thin films 101 and 102 are changed and the voltage changes corresponding to the amounts of the change of the electrical resistance are produced across both ends of the MR thin films 101 and 102. Information signals are reproduced by detecting these changes in voltage.
FIGS. 7A and 7B show MR curves of the MR thin films 101 and 102, with the length L of the MR films 101 and 102 along the direction x being 20 .mu.m and with the length W of the MR films 101 and 102 along the direction y being 6 .mu.m. In FIG. 6, the lengths L and W are shown only for the MR thin film 102. FIGS. 7A and 7B show the MR curves for the sense current of 10 mA and the sense current of 1 mA, respectively.
With the above-described MR head, attempts have been made towards reducing the width of the two gaps defined by insulating layers between a pair of magnetic shield cores and the MR device, that is the playback gaps.
With the above MR head, the two playback gap are not necessarily equal in size, but often are different from each other.
If the gap width is further reduced in such an MR head, the one of the two MR thin films making up the MR device which is closer to the magnetic shield core is magnetically Coupled to the magnetic shield core and becomes a magnetically thick film, so that the probability becomes high that the MR effect becomes unbalanced between the two MR thin films.
This has been confirmed by the fact that, if the MR device of the MR head is constituted with one MR thin film, the MR device is magnetically coupled to be closer to one of the magnetic shield cores, such that the MR device has a sole magnetic domain to stabilize the behavior of the MR device.
FIG. 8 shows the results of calculations of changes in the ratio of magnetization of two MR thin films making up the MR device when one of the gap widths of the MR head is changed. The ratio of magnetization is expressed as the ratio of magnetization. (.phi..sub.3), the gap width for which has been changed, to magnetization, (.phi..sub.4) of the remaining MR thin film. In the drawing, the abscissa, and the ordinate denote the gap width and the ratio of magnetization .phi..sub.3 /.phi..sub.4, respectively.
The results of FIG. 8 show that, if one of the gap widths is not larger than about 0.3 .mu.m, the ratio of magnetization of the two MR thin films cannot reach 60%, so that magnetization of the MR thin film the gap width for which has been changes is not sufficient. That is, the MR thin film is magnetically coupled with the magnetic shield core to form a magnetically thick film, thus unbalancing the magnetization between the two MR thin films, in other words, unbalancing the MR effect.
If the MR effect of the two MR thin films making up the MR device is unbalanced, Barkhausen noise tends to be produced to render the output unstable.
FIGS. 9A and 9B show MR curves when the MR effect of the two MR thin films making up the MR device is intentionally-unbalanced. FIG. 9 shows an MR curve of the external magnetic field derived from experimentation. FIG. 9B shows an MR curve derived from simulation. It is seen from the results of FIG. 9B that skipping occurs in the region of lower intensity of the magnetic field, as indicated by encircled area S. Thus, it is seen that if the MR effect between the two MR thin films is unbalanced, the Barkhausen noise is produced to render the output unstable.